The invention relates to surface preparation, processing and cleaning, of workpieces, such as semiconductor wafers, flat panel displays, rigid disk or optical media, thin film heads, or other workpieces formed from a substrate on which microelectronic circuits, data storage elements or layers, or micro-mechanical elements may be formed. These and similar articles are collectively referred to here as a xe2x80x9cworkpiecexe2x80x9d.
Surface preparation, such as cleaning, etching, and stripping, is an essential and important element of the manufacturing process for semiconductor wafers and similar workpieces. Surface preparation steps are commonly performed, using liquid corrosive, caustic, or solvent chemicals, or using vapor phase chemicals. Surface preparation of workpieces is performed to prepare or condition the surface for a subsequent process step.
Cleaning is a critical step in manufacturing semiconductors and similar products. Cleaning involves the use of chemical formulations to remove contaminants, such as oxides, particles, metals, or organic material, while maintaining the cleanliness and integrity of the surface of the workpiece. Some liquid, gas or vapor phase chemicals when applied to a workpiece, result in surface characteristics that are more susceptible to contamination than others. For example, application of hydrofluoric acid (HF) to the surface of a workpiece will remove oxide from the silicon surface, resulting in a surface that is active. Workpieces in general, and especially workpieces having an active surface, are constantly susceptible to contamination by airborne microscopic particles. Contamination can also occur in the cleaning process, when the liquid process media is removed from the surface of the workpiece.
Thus, to m contamination of the workpiece, it is advantageous to perform a sequence of surface preparation steps within a controlled environment, that preferably occupies a relatively small amount of fabrication facility space, and in which exposure to contamination sources is
Cleaning workpieces while avoiding or minimizing contamination has long been an engineering challenge. Workpieces are often cleaned with a spray or bath of de-ionized water. The water is then removed, often in the presence of an organic solvent vapor, such as isopropyl alcohol, which lowers the surface tension of the water. This helps to prevent droplets of water from remaining on and contaminating the workpiece.
Various cleaning methods and systems and various rinsing and drying methods and apparatus have been proposed and used. In a typical system, wafers are immersed in a vessel. A mechanism is provided to hold the wafers. Another mechanism is provided to lift the wafers out of the liquid, by pushing them up from below. While this technique has been used, it can result in trapping of liquid in or around the spaces where the wafers contact the holding mechanism, resulting in increased contamination. In an alternative system, the wafers are held in a fixed position while the liquid is drained away from below. This technique has less tendency for trapping liquid. However, as the liquid level drops, the solvent vapor above the liquid is absorbed by the liquid. Consequently, the top sections of the wafer are exposed to liquid which is different from the liquid at the bottom sections of the wafers. This potentially results in non-uniform processing. Accordingly, while these and other techniques have been used with varying degrees of success, there is still a great need for improved systems and methods for cleaning workpieces.
To these ends, in a first aspect, surface preparation processes on a workpiece are performed within a single chamber. The workpieces are contacted by process fluids by spraying or immersion. The workpieces may be processed and/or rinsed and dried within the single chamber. This minimizes exposure of the workpiece to contaminants and provides an improved application of process fluids or media to the workpiece.
In a second aspect, workpieces are held stationery in a fixed support. A process chamber around the fixed support can pivot to move a drain outlet or edge down to the level of the liquid contained in the chamber. The liquid then drains out of the chamber over the edge or through the outlet. The process chamber provides for containment of process fluid. An optional second or outer containment chamber provides for containment and disposal of process fluid, and for isolating the process environment from the ambient environment, human operators, and adjacent parts and equipment.
In a third aspect, openings or spray nozzles on or in the process chamber, or on the fixed support, supply a fluid onto the workpieces. This allows for versatile processing.
In a fourth aspect, sonic energy, such as ultrasonic or megasonic energy, is applied to the workpiece, preferably through liquid in which the workpiece is immersed. Use of sonic energy can provide for faster and more effective processing.
In a fifth aspect, an outer chamber is provided around the process chamber. The outer chamber may be purged with a gas and/or vapor to maintain a desired environment around the workpieces.
In a sixth aspect, unique methods and apparatus are provided for cleaning a workpiece such as a semiconductor wafer. These methods and apparatus help to solve the problems of the apparatus and methods now used in the semiconductor manufacturing industry. Workpieces are held in a fixed support within a process chamber having a drain outlet. The workpieces are immersed in liquid within the process chamber by filling the chamber with liquid, preferably from one or more outlets near the bottom of the chamber. Liquid is preferably continuously supplied into the chamber so that liquid is continuously overflowing and running out of the drain outlet. The process chamber is pivoted to move the drain outlet down in a controlled movement, to lower the level of liquid in the chamber. Liquid supply to the chamber and overflow at the liquid surface preferably continues as the chamber pivots and the liquid level drops. This process continues until the liquid level drops below the workpieces and the chamber is pivoted to drain virtually all liquid out of the chamber.
By maintaining the overflow at the liquid surface, and by maintaining a constant flow towards and out of the drain outlet, impurities at the liquid surface flow away from the workpieces, reducing potential for contamination. The liquid in the chamber remains uniform at all depths, as the surface of the liquid which the solvent vapor dissolves into, is constantly being replaced with fresh liquid. Consequently, improved cleaning is provided with a uniform liquid bath. Disadvantages associated with the machines and methods currently in use, as described above, are reduced.
The aspects of the invention described above provide greatly improved processing and cleaning apparatus and methods. These aspects help to provide more reliable and efficient processing.
Further embodiments and modifications, variations and enhancements of the invention will become apparent. The invention resides as well in subcombinations of the features shown and described.